1. Field of the invention
The present invention generally concerns transmission systems designed to contribute to the rotational coupling of one shaft to another.
2. Description of the prior art
It is more particularly directed to transmission systems such as these which comprise, on the one hand, an annular member, hereinafter referred to for convenience as the input member, which is adapted to be keyed at least circumferentially to a first of the shafts concerned, in practice a driving shaft, and which features a generally cylindrical axial wall and a generally transverse radial wall, and, on the other hand, within the internal volume of said cylindrical wall, a movement take-up device keyed axially and circumferentially to the input member and at least circumferentially to the second of the shafts concerned, in practice a driven shaft.
A transmission system of this kind may, for example, form part of a hydraulic coupling unit, in particular for automobile vehicles, in the form of a torque converter or a hydraulic coupling.
A hydraulic coupling unit of this kind generally comprises an impeller wheel and a cover which, itself comprising a generally cylindrical wall and a generally transverse wall, is fastened to the impeller wheel and forms with the outside wall of the latter a casing in which are disposed in particular, facing the impeller wheel, a turbine wheel and, within the internal volume of its cylindrical wall, between its transverse wall and said turbine wheel, a movement take-up device.
In the case where it is required to filter out at this point vibrations which may arise in the kinematic system into which the assembly is inserted, this movement take-up device is a torsional damper device which itself comprises two coaxial parts disposed to rotate relative to one another against elastic means disposed circumferentially between them and a first of which parts, hereinafter referred to for convenience as the input part, is keyed to the input member whereas the second of said parts, hereinafter referred to for convenience as the output part, is adapted to be keyed to the driven shaft concerned.
One of the problems to be overcome in implementing hydraulic coupling units of this type is to achieve under good conditions the axial and circumferential keying of the input part of the torsional damper device to the input member which the cover of the assembly constitutes.
In this instance, the problem results in particular from the fact that the component parts to be employed to achieve this are operative in an extremely congested environment, the amount of space available axially and radially being particularly limited.
Thought might be given, for example, to fastening to the transverse wall of the cover, as by welding or riveting, one of the component parts of the input part of the torsional damper device.
When riveting is employed, the necessary rivet may be drawn from the wall itself of the cover, to preserve the fluid-tightness of the assembly, although this is at the price of a certain degree of complexity.
When welding is used, an additional difficulty has to be overcome and is due to the fact that, although the wall of the cover concerned is of mild steel, for example, which can usually be welded, the same does not apply to the component parts of the input part of the torsional damper device, as these are usually of treated steel, for example, in the most usual situation, a steel which has been hardened by carbonitriding.
Moreover, in both cases the transverse wall in question of the cover consists of a portion of the cover which, in operation, is subjected to the highest mechanical stresses and which is therefore likely to be subjected to non-negligible deformation prejudicing the strength of the riveting and/or welding that may have been applied to it.
Given what has been said, it has also been proposed to link the input part of the torsional damper device to the cylindrical wall of the cover, where the stresses are lower, and to use for this purpose lugs fixed at one end to said input part and at the other end to said cylindrical wall of the cover.
In practice, in order to be weldable to the cylindrical wall of the cover, these lugs are made of mild steel and they are only fastened to the part concerned of the input part of the torsional damper device after this has had applied to it the carbonitriding treatment needed to harden it.
Apart from the fact that a process of this kind inevitably entails costly handling after such treatment, for the purposes of the fixing to be achieved, such fixing can only be done by riveting.
The use of rivets requires a non-negligible area for mounting them, which is inevitably detrimental from the point of view of the overall diameter of the assembly and which may prove unacceptable in certain applications, in particular those in which use is made, for the elastic means disposed circumferentially between the two parts of the torsional damper device, of coil springs which must be of significant circumferential extent to procure an equally extensive range of movement between said parts.
Also, in implementing hydraulic coupling units with integrated movement take-up devices of the type concerned, a further difficulty results from the fact that, independently of the previous problem of fixing the input part of the movement take-up device to the cover, it is desirable that the placing of the latter in said cover is effected by simple axial insertion into the cover, and that this be done autonomously, by means of a subassembly made up beforehand.
A general object of the present invention is an arrangement which, while enabling this requirement to be satisfied, also provides a satisfactory and simple means of overcoming the problems oulines hereinabove.